1. Field of the Invention
The present invention relates generally to automated control of a laser head for treatments on human skin, and more particularly to automated control of a laser head for laser debridement of burns.
2. Prior Art
Thermal burns and vesicating (blistering) due to chemical warfare agents such as sulfur mustard and Lewisite induced skin injuries can vary in severity between second degree and third degree. Vesicant injuries in particular can take several months to heal, necessitating lengthy hospitalizations, and result in significant cosmetic and/or functional deficits.
The initial step in the repair of a thermal or chemical burn wound is to remove the dead skin, called wound debridement, and replaces it with a viable biological dressing. Autologous skin from another site of the patient, in the form of a split thickness skin graft is the method of repair that is most often employed. In special circumstances a flap of muscle with its attached blood supply may be used to cover severely burned areas that lack sufficient blood supply to allow the split thickness graft to become engrafted.
It has been shown that early excision at less than one week after the burn significantly reduces blood loss. Later excisions after 7-10 days are associated with significantly greater blood loss. The reason for this is that the very presence of the dead skin causes an inflammatory reaction which results in a significant increase in blood flow to the skin. Consequently, when burned skin is excised from the body after 7-10 days there is a much greater blood loss. Others have analyzed the survival rates after burns over a 50 year period and concluded that prompt excision of the eschar after the burn occurred was largely responsible for reducing the mortality after burns, and resulted in a significant improvement of survival rate.
It is, therefore, apparent that early excision of the burn and immediate coverage of the wound with a biologic dressing, preferably autologous skin, if it is available, is the optimal method for caring for the thermal and chemical burn wound.
There are various methods of wound debridement. The method of wound debridement that is most commonly used is surgical excision using stainless steel cutting blades, which can be mounted on different types of handles and into which are built methods of controlling the depth of the excision. The excision may be superficial, as in a deep dermal burn, by cutting off the injured tissue through the appropriate level of the dermis; or in the case of a full thickness burn, the entire skin: i.e., epidermis and dermis may be cut off either leaving the subcutaneous tissue or the fascia exposed. This method of using a steel blade as a cutting instrument works well in the hands of a well trained surgeon. However this method is time consuming in large burns and is often associated with the loss of considerable amounts of blood. The least amount of blood is lost when the entire thickness of skin and subcutaneous tissue must be excised. The reason for this, is that in this setting the individual blood vessels arising from the deeper tissues can be identified and can be ligated before they enter the skin. Whereas excisions through either superficial or deeper dermis are associated with significantly more bleeding, since the distinct nutrient vessels which arise from the deeper tissues have arborized into numerous branches as they progress towards the surface of the skin.
Until recently, the standard method for burn debridement, as stated earlier has been the use of stainless steel blades. Recent advances have been made in improving the healing of thermal and chemical burns using a variety of techniques to debride damaged tissue, including the use of medical lasers. One promising modality for excision (debridement) uses a laser beam. Excision using a laser beam would be associated with significantly reduced morbidity, since the amount of blood lost when a laser beam is used has been shown to be significantly reduced. It is important to note also that the percentage of successful wound closures after the excision using grafts is the same irrespective of whether a laser or a steel knife was used to remove the eschar. Laser vaporization of full thickness burn eschar in a porcine model with immediate engraftment was shown to be associated with minimal blood loss and equal graft take.
Current uses of lasers in dermatological practice as well as the types of lasers used for each specific procedure are well known. They include CO2 and Er:YAG lasers as being the most appropriate for cutaneous resurfacing.
The CO2 laser emits radiation at a wavelength of 10,600 nm. The fluence should exceed the vaporization threshold of skin (5 J/cm2)4,5 and the pulse duration (or its scanning laser equivalent, the ‘dwell time’) should be shorter than the τ (695-950 ms) although pulse widths of up to 1 ms appear to be acceptable in vivo. At lower fluences there is more desiccation and carbonization and a higher likelihood of scarring. The depth of vaporization and thermal necrosis depend on the fluence, dwell time and number of passes. Two different laser systems are in common use. High energy pulsed lasers produce wide diameter pulses with beam diameters of up to 3 mm. A computerized pattern generator can be used in the treatment of relatively large areas. With low energy scanned focused beams, a computer-controlled mirror rapidly scans a focused beam across a predetermined area. The dwell time is 300-900 ms depending on the depth of damage required. Clinical outcomes using these two different types of system can only be compared if the fluences and number of passes are considered.
The Er:YAG (erbium:yttrium-aluminium-garnet) lasers produce radiation (λ=2940 nm) with a higher absorption coefficient for water than the CO2 laser and a lower optical penetration depth (1 μm and 20 μm, respectively). Because ablation is inversely proportional to the optical penetration depth, Er:YAG lasers require a lower fluence for tissue ablation. This is a largely photoaccoustic rather than a photothermal reaction. The depth of vaporization is 2-4 μm for each 1 J/cm2 fluence and very superficial peels may be achieved. Epidermal lesions can be ablated accurately, but deeper peels may be limited by intraoperative bleeding due to the relatively thin layer of residual thermal damage. Attempts to improve haemostasis have been made by adapting the Er:YAG laser to produce longer pulses and/or lower fluences or through combination with low-fluence CO2 or with secondary Er:YAG lasers. Side-by-side comparisons suggest that for the same depth of injury, re-epithelialization time and persistence of erythema is shorter in sites treated with the Er:YAG as opposed to the CO2 laser. However, the thickness of subsequent fibrosis or ‘collagen remodeling’ is greater in CO2 laser-treated sites, possibly reflecting greater underlying thermal damage.
Er:YAG lasers have been used for a wide variety of procedures, ranging from facial resurfacing to burn debridement. They have been shown to be particularly useful in the debridement of partial-thickness thermal burns and in the management of deep Lewisite injuries. A review of the literature clearly indicates that laser debridement produced equally good results with excisions performed with a steel blade. In addition, unlike the Gaussian beam profiles created by CO2 lasers, Er:YAG laser beams tend to be uniform and produce uniform depths of ablation. Thus, it can be concluded that the use of erbium:yttrium-aluminum garnet (Er:YAG) laser in the skin resurfacing to debridement of deep partial thickness burns, including those caused by sulfur mustard have demonstrated benefits of this method of excision.
It is noted that debridement with Er-YAG and CO2 lasers promise to provide great benefits in the treatment of leg ulcers (e.g., venous stasis ulcers, pressure ulcers, diabetic foot ulcers). Additionally, leg ulcers (e.g., venous stasis ulcers, pressure ulcers, diabetic foot ulcers) and penetrating injuries to the skin can require frequent debridement to help these wounds to heal.
Lasers have a wide range of applications in dermatology. Such procedures include removal of hair, tattoos, freckles, wrinkles, acne, sun-damaged skin, scars—including surgical and acne scarring, facial red veins and other vascular lesions, skin resurfacing and malformations (such as port wine stains) and hair and tattoo removal. Lasers are also being used or investigated for removal of keloids and hypertrophic scars as well as viral warts, seborrhoeic keratoses, skin cancers, and psoriasis plaques.
One major drawback of all currently available laser systems is that they require the physician and/or surgeon to move a hand piece over the damaged area, which is very time-consuming given an injury with a large surface area. The process also requires a skilled physician/surgeon, and a steady hand. The design of small hand held scanners on the ends of articulated arms has weakened this drawback to a limited extent. However, the scanned areas are relatively small and the physician/surgeon still needs to move the scanner head over relatively large treatment areas. A time savings could be realized with a system that could scan very large areas of a patient's body and perform precise laser treatment, such as debridement automatically and quickly with minimal physician/surgeon/technician involvement. In fact, certain laser treatment processes are so slow that they are effectively impractical for treating patients. This is the case, for example, for erbium:YAG lasers used for laser debridement of chemical and thermal burn injuries. For the latter applications, such a system would greatly decrease medical logistical burden, especially in a mass casualty scenario.
In the present disclosure, the various embodiments of the present invention are described in terms of their application for laser debridement of chemical or thermal burns. However, it is appreciated by those familiar with the art that the described embodiments can also be used as automated systems for a number of other skin treatments such as for removal of hair, tattoo, freckle, wrinkle, acne, sun-damaged skin, acne scarring facial red veins and other vascular lesions and malformations (such as port wine stains) with minimal effort. Such lasers treatments have also shown great promise for removal of keloids and hypertrophic scars as well as viral warts, seborrhoeic keratoses, skin cancers and psoriasis plaques.
It is also appreciated by those skilled in the art that the described embodiments of the present invention are modular in design so that each component of the system and its operating software could be readily updated and upgraded.